Method of making electric bulbs



Aug. 1969 HAJIME SHlRAGAKI I 3,460,219

METHOD OF MAKING ELECTRIC BULBS Filed ocn'ls. 1966 United States Patent 3,460,219 METHOD OF MAKING ELECTRIC BULBS Hajime Shiragaki, Tokyo, Japan, assignor to Ichitaro Fukui, Ota-ku, Tokyo, Japan Filed Oct. 18, 1966, Ser. No. 587,568 Int. Cl. H01j 9/18 US. Cl. 2925.13 1 Claim ABSTRACT OF THE DISCLOSURE This invention relates to methods for making electric bulbs and more particularly to methods for making small or very small electric bulbs.

FIG. 1 is a vertical sectional View of a conventional small electric bulb,

FIG. 2 is a vertically sectional view of electric bulb component parts assembled according to the present invention,

FIGS. 3 and 4 are a vertically sectional view and plan view of a jig to be used in the present invention, respectively,

FIG. 5 is a vertically sectional view of a heating furnace to be used in the present invention,

FIG. 6 is a vertically sectional view of an electric bulb completed with the component parts shown in FIG. 2,

FIG. 7 is a vertically sectional view showing another example of electric bulb component parts assembled according to the present invention, and

FIG. 8 is a vertically sectional view of an electric bulb completed with the component parts shown in FIG. 7.

In a conventional small or very small electric bulb, as

illustrated FIG. 1, two sealed lead wires 1 and 2 are first 40 surrounded with glass to form a stem 3, and a tungsten filament 4 is fixed to the tips of the sealed lead wires. Thereafter an encloser 5 is applied to cover the above components and is sealed with the stem 3. In sealing, the components, an exhaust part 6 is made in a part of the encloser 5. Then, such semiproduct of an electric bulb is connected to an exhausting stand, the interior of the encloser is exhausted, an inert gas is enclosed as required and the exhaust part 6 is sealed and cut at 7 so that a completed product may be obtained.

In the conventional manufacturing method, as described above, not only many steps are required but also specifically the steps of forming the stem and sealing the encloser are so difficult to automatically execute because the dimensions of the respective parts are small so that it is usual for those steps to be still carried out by hand by skilled glass workers. Therefore, the efliciency and output are low, with the greater part of the production cost being occupied by labor and therefore the price of the product is very high.

The present invention is to eflfect in one step the various steps of forming the stem, sealing the encloser, exhausting the encloser, enclosing the gas and sealing the exhaust part without requiring any skilled worker by using simple parts which can be mass-produced so that the number of steps may be materially reduced, labor may be greatly saved and uniform products may be cheaply mass-produced.

The present invention will be explained with reference to an embodiment shown in FIGS. 2 to 6.

11 and 12 are lead wires and a tungsten filament 13 is fixed to their tips in advance. Then, fine glass tubes 14 3,460,219 Patented Aug. 12, 1969 and 15 are fitted to the lead wires 11 and 12, respectively, and are inserted into a glass encloser 16 so as to be positioned near the opening. Thus, a semiproduct 17 is assembled as shown in FIG. 2. This condition is kept by 5 the friction between the respective parts.

Then, such semiproducts 17 are contained in inverted condition in respective holes or recesses 19 provided in the upper surface of a jig 18 as shown in FIG. 4. The jig 18 is formed of a heatproof material which will not be fused with glass as carbon or graphite or is formed by coating the surface of a heatproof metal with a material which will not be fused with glass. The hole 19 has a diameter substantially equal to that of the encloser 16 and a depth lesser than the height of the encloser 16.

Therefore, when the semiproduct 17 is inserted into the hole 19, a part of the encloser 16 and fine glass tubes 14 and 15 will be exposed from the hole as shown in FIG. 3.

The jig 18 supporting the semiproducts 17 in such condition is inserted into a furnace as is shown in FIG. 5.

20 The furnace has a furnace tube 20 made of a heatproof material as quartz or metal. A heating resistance wire 22 is wound around a heating part 21 in the middle of the furnace tube 20. The heating part 21 is enclosed with heat insulating material 23 such as magnesia. Further,

an enclosing wall 24 is provided outside the heat insulating material 23. 25 and 26 are pull-out terminals of the heating resistance wire 22 provided on the enclosing wall 24. Doors 29 and for intercepting outside air are provided in an inlet 27 and outlet 28 of the furnace tube 20,

30 respectively. An exhaust part 31 for evacuating the furmetal wire 34 for moving the carriage 33 from the inlet 27 to the outlet 28 is fixed to the carriage.

The jig 18 is mounted on the carriage 33 and is placed in the heating part 21 within the furnace tube 20 by the operation of the metal wire 34. The inlet 27 and outlet -28 are closed. The furnace tube 20 is exhausted to a vacuum through the exhaust part 31. Then, due to the radiant heat from the inside wall of the furnace tube, the temperature of the exposed glass part of the semiproduct 17 will quickly rise. However, the heat capacity of the jig 18 is so large that the rise of the temperature of the jig will be slow. Therefore, the part of the semiproduct 17 in the hole 19 is hard to heat. If the exhaust part 31 is closed and an inert gas is fed into the furnace tube through the inlet part 32 at a proper time, the inert gas 0 will also enter the encloser 16 of the semiproduct. The

temperature of the exposed part of the semiproduct 17 will continue to rise even thereafter. Finally, the glass part will melt, and a stem 35 as is shown in FIG. 6 will be formed while at the same time a sealing will be effected. Thereafter, the carriage 33 is moved out of the heating part 21 by the operation of the metal wire 34 and is gradually cooled. After it is properly cooled, the door 30 is opened and the carriage is moved out of the furnace tube 20. Then the completed gas-filled electric bulbs as illustrated in FIG. 6 will be obtained.

In case it is not necessary to enclose an inert gas in the electric bulb, the above described feeding of the inert gas will not be required and only the exhausting operation will suffice. Further, the exhausting operation may be omitted and the inert gas may be constantly introduced into the furnace tube 20. In such case, no doors will be required for the inlet 27 and outlet 28 and therefore it will be possible to continuously carry out the production by constantly inserting the semiproducts supported by the jig into the furnace tube. Further, in the case of producing electric bulbs for such low class uses as for models,

it will not be necessary to keep the interior of the furn'ac'e tube 20 at a vacuum or in an inert gas atmosphere. Even if air is present in the completed electric bulb as a result, the amount of air will be so small that the bulb can light.

Further, the semiproduced electric bulb to be inserted into the above described furnace may have a structure such as in FIG. 8 instead of the structure in FIG. 2. That is to say, a glass disk 38 having small holes 36 and 37 through which the lead wires 11 and 12 are to be inserted, respectively, can be used instead of the fine glass tubes 14 and 15 in FIG. 2. Even though such glass disk 38 is used, the above described manufacturing method can be carried out. FIG. 7 shows a thus completed electric bulb. 39 is a stem formed by melting the disk 38.

As evident from the above explanation, according to the present invention, as the component parts to be used have simple shapes, they can be easily mass-produced, with such various steps as forming the stem, sealing the encloser, exhausting the encloser, enclosing the gas and sealing the exhaust part being effected in one step simultaneously for many electric bulbs and the operation requires no skilled labor. Therefore, uniform products of the same contour dimensions can be mass-produced at a low cost. Thus the present invention is effective as applied specifically to the manufacture of small or very small electric bulbs which have been difiicult to manufacture.

What is claimed is:

1. A method for making electric bulbs comprising the steps of forming a semiproduct having lead wires, a filament, and a glass enclosure for the wires and filament provided with an open end, positioning the semiproduct in a recess in a member having a comparatively large heat capacity yet not capable of being fused with glass with the open end and portions to besealed being exposed, positioning the member and semiproduct within a heating Zone, developing a vacuum in the heating zone, introducing an inert gas into the heating zone which enters the enclosure through the open end and after which the exposed portion melts to form a seal about the wires, removing the member and semiproduct from the heating zone, and cooling the member and semiproduct to provide a gas-filled electricbulb.

s. LEON BAsEoriE, Primary Examiner SAUL R. FRIEDMAN, Assistant Examiner US. Cl. X.R. 

